Factors associated with alveolar bone depth mesial to the mandibular third molars after orthodontic protraction

Abstract

The objective of this research was to study the factors associated with the alveolar bone depth mesial to the mandibular third molars (M8) after the mandibular second (M7) and third molars were protracted into the space of the mandibular first molars (M6), which were newly extracted for orthodontic treatment or extracted more than 1year before treatment. This retrospective study included 57 adult patients (mean age 23.40±4.40years) in whom M6 were newly extracted for orthodontic treatment or extracted more than 1year before treatment. The alveolar bone depth mesial to M8 was measured on posttreatment panoramic radiographs. The vertical, horizontal, and angular changes of M8 were measured on both pre- and posttreatment panoramic radiographs. Linear correlation and regression analyses were conducted to explore the factors associated with the alveolar bone depth mesial to M8. The alveolar bone conditions of M6 (R= -0.391, P<0.001) and the vertical movement directions of M8 (R= -0.433, P<0.001) were significant factors associated with the alveolar bone depth mesial to M8 after orthodontic protraction. Without considering the pretreatment periodontal status of M8, patients with M6 extracted exceeding 1year before treatment and with M8 extruded after orthodontic protraction may exhibit deeper alveolar bone depth mesial to M8.